Various coordinate locating devices for locating the coordinates of an object are known. Some coordinate locating devices can detect the coordinates of an object from a pointing instrument, such as a pen, a fingertip, or a specific device for use with such devices. Accordingly, a user can input information with the pointing instrument.
Common techniques employed in conventional coordinate locating devices for locating the coordinates of an object include mechanical buttons, crossed light beams, acoustic surface waves, capacitance sensing, and resistive materials. Among these devices, those employing crossed light beams are not limited by the display panel size and are therefore cost competitive.
For example, Griffin, U.S. Pat. No. 4,820,050 discloses a solid-state optical position determining apparatus having an LED light source and an image sensor. However, the apparatus can only locate the coordinates of one object, resulting in undesirably limited applications.
Another example is an apparatus disclosed by Segen, U.S. Pat. No. 5,484,966, entitled “Sensing stylus position using single 1-D image sensor.” The apparatus utilizes two mirrors and one image sensor, but can only locate the coordinate of one object.
To solve the problem with the above two conventional techniques, US Patent Publication. No. 2009/0,066,662 by Liu Yun-Cheng, et al. proposes a system capable of distinguishing multiple touch points, and US Patent Publication. No. 2008/0143682 by Shim, Yeon Shim, et al. also proposes a display device having a multi-touch recognition function. However, both require at least three image sensors, which greatly increases manufacturing costs.
To deal with the above drawbacks, U.S. patent application Ser. No. 12/700,598 provides a coordinate locating apparatus capable of locating the coordinates of multiple objects by utilizing only two detectors and a mirror to detect mirrored images of the objects, thereby reducing manufacturing costs. However, the complexity of calculation increases with the number of touch points to be located.